This is a proposal to utilize Tax transgenic animals to enhance our understanding of principles of molecular oncology that govern development of HTLV-1 associated neoplasia that are broadly applicable to many forms of neoplasia. Our previous studies have shown that tumors in Tax transgenic mice are resistant to the induction of apoptosis after gamma irradiation. Since Tax inactivates p53 and activates NFkB, we will examine if these findings explain the effects on apoptosis or whether another mechanism is involved. Aim 1 how does HTLV infection affect apoptosis? 1a. Is the canonical or non-canonical NF kB pathway important for resistance to apoptosis? 1b. Which NFkB inducible genes are responsible for resistance to apoptosis 1c. Is resistance to apoptosis due to induction of FLIP, bcl-XL, A1, or IAP2 or another mechanism? 1d. is resistance to apoptosis a direct or indirect effect of Tax expression? We will further examine the role of p53, in light of the studies in Aim 1 and our previous studies that Tax transgenic p53 heterozygous mice as compared to Tax transgenic, p53 homozygous wild type mice exhibited more rapid tumor dissemination. Aim 2. What is the contribution of loss of p53 function to HTLV tumorigenesis? 2a. Are p53 transcriptional transactivation properties disrupted in Tax transgenic mice? 2b. Is p53 mutated, deleted, or repressed with tumor dissemination? 2c. What biological differences account for altered tumor dissemination in p53 mice? One central and unanswered question is why is HTLV-1 so highly specific for transformation of lymphoid compartment cells. Aim 3. What regulates the cell-type specificity of HTLV transformation? What is the role of IL15 in Tax transgenic animals?